JP-A-2005-265482, JP-A-2003-314262, JP-A2006-070835, and JP-A-2005-256832, disclose valve devices each being applied to a secondary air supply system, as an example. The secondary air supply system leads fluid such as secondary air discharged from an air pump into an exhaust pipe upstream of a catalyst, which is provided for cleaning exhaust gas. In this operation, the secondary air supply system accelerates activation to warm up the catalyst by supplying the secondary air to the upstream of the catalyst for purifying exhaust gas.
The valve device includes a first fluid channel, a second fluid channel, a control valve, a check valve, and a pressure sensor. The first fluid channel is connected to a discharge port of the air pump. The second fluid channel is connected to the exhaust pipe in upstream of the catalyst. The control valve opens and closes a communication passage between the first and second fluid channels. The check valve restricts backflow of the exhaust gas toward the control valve through the second fluid channel. The pressure sensor detects pressure in the first fluid channel. The pressure sensor is used for detecting a malfunction or control of an air-fuel ratio.
In the detection of a malfunction, an operating condition of the air pump and a malfunction caused by seizure of the control valve are diagnosed based on a correlation between a driving condition of the air pump, an opening and closing condition of the control valve, and detected pressure of the pressure sensor. In the control of the air-fuel ratio, the amount of secondary air supplied from the air pump to upstream of the catalyst is calculated based on the detected pressure of the pressure sensor in order to properly maintain an air-fuel ratio of the catalyst.
As shown in FIG. 4, a pressure sensor J1 disclosed in JP-A-2005-265482 employs a structure where the pressure sensor is attached to a top of an electromagnetic solenoid J2 of a control valve for detecting pressure in a first fluid channel J3 extending through the interior of the electromagnetic solenoid J2. In this structure, pulsation in pressure in the first fluid channel J3 is transmitted to the pressure sensor J1 after being attenuated, and consequently, malfunction is hardly detected according to pulsation in pressure.
As shown in FIG. 5, a pressure sensor J1 disclosed in JP-A-2003-314262 employs a structure where pressure in a first fluid channel J3 is transmitted to the pressure sensor J1 through a conduction pipe J4. However, since the conduction pipe J4 is communicated with the axis of the first fluid channel J3, the pressure sensor J1 is easily affected by a flow of secondary air fed from an air pump.
Therefore, the pressure sensor J1 may be affected by a shock wave occurring in the first fluid channel J3, and consequently, an accuracy of pressure detected using the pressure sensor J1 becomes low.